This invention relates generally to synthetic ester basestock blends based on polyneopentyl polyol (xe2x80x9cPNPxe2x80x9d) esters and, more particularly, to basestocks including PNP esters mixed with a coupling agent to increase compatibility with standard lubricant additive packages and provide a highly biodegradable lubricant formulation suitable for use in 2-stroke engines.
There is a continuing need to provide lubricant compositions which are highly biodegradable and are fully miscible with gasoline. This is particularly true with respect to lubricants for 2-stroke engines. These engines are often small gasoline engines used in recreational vehicles, such as motorboats, mono-skis for water use, snowmobiles and in lawn equipment. Thus, all such uses are in sensitive environments subject to pollution. Absent an acceptable biodegradabability level, exhaust and leakage of fuel mixed with the lubricant would tend to pollute forests, rivers, lakes and other waterways.
In order for lubricants for 2-stroke engines to be acceptable, they must provide a high viscosity index, acceptable biodegradability, miscibility with gasoline and be compatible with standard lubricant additive packages. Suitable viscometrics include good cold flow properties, such as a pour point less than about xe2x88x9240xc2x0 C. and a viscosity at xe2x88x9240xc2x0 C. of less than 36,000 cps and a suitably high flash point, greater than about 240xc2x0 C.
Biodegradability is measured pursuant to ASTM- 5864 which is similar to the accepted Modified Sturm test adopted by the Organization for Economic Cooperation Development in 1979. These biodegradability tests involve the measurement of the amount of CO2 produced by the test compound, which is, in turn, expressed as a percent of the theoretical CO2 the compound could produce calculated from the carbon content of the test compound. The test is performed to measure released CO2 trapped as BaCO3 and is well known to those in the art and will not be set forth herein in detail. However, the generally accepted ASTM test procedure is incorporated herein by reference.
Generally, lubricants having a biodegradability of over 60% pursuant to ASTM-5864 or the Modified Sturm test are considered to have acceptable biodegradability characteristics.
Examples of biodegradable basestocks based on branched chain synthetic esters and lubricants formed therefrom are disclosed in U.S. Pat. No. 5,681,800. Here, branched chain fatty acids provide the desired viscometrics, low temperature properties, lubricity, biodegradability and solubility of additives therein.
While such biodegradable products are available, it remains desirable to provide a synthetic ester basestock providing all these desirable properties without the use of significant amounts of esters of branched chain acids which do not biodegrade as readily as esters based on straight chain acids.
Generally speaking, in accordance with the invention, improved synthetic biodegradable polyneopentyl polyol (xe2x80x9cPNPxe2x80x9d) based ester basestocks and lubricants including conventional additive packages soluble therein are provided. The synthetic ester basestocks include PNP esters mixed with a coupling agent to aid in solubility of standard lubricant additive packages in the basestock. The PNP ester and coupling agent may then be blended further with lesser amounts of at least one additional high molecular weight linear or branched chain ester. The additional high molecular weight synthetic ester may be a polyol ester of a linear or branched chain monocarboxylic acid, a dicarboxylic acid ester of linear and/or branched chain monoalcohols, a linear and/or branched monocarboxylic acid ester of linear and/or branched chain monoalcohols, or mixtures thereof.
The PNP ester-coupling agent component of the basestock is a mixture of a polyneopentyl polyol ester, such as a polypentaerythritol ester (xe2x80x9cpoly PE esterxe2x80x9d) and a coupling agent. The coupling agent is a compound of intermediate polarity between a hydrocarbon and the polyneopentyl polyol ester, such as esters having an oxygen content from about 4 to 16 weight percent, preferably from about 7 to 13 weight percent. In the preferred embodiment of the invention the coupling agent is an ester which is the reaction product of a dicarboxylic acid having between about 18 to 36 carbon atoms and a mono-alcohol having between about 6 to 14 carbon atoms. Most preferably, the coupling agent is a dimer acid ester which is the reaction product formed by the esterification of dimer acid with a monoalcohol, such as 2-ethylhexanol.
The PNP ester is present in the PNP ester-coupling agent mixture between about 55 to 80 weight percent. The preferred lubricant basestock also includes additional esters blended with the PNP ester and coupling agent mixture. The additional esters are added to adjust the viscometrics of the basestock and modify the lubricity and fluidity of the blend. Typically, the lubricant basestock includes between about 65 to 85 weight percent of the PNP ester-coupling agent mixture with the additional esters being the linear and/or branched chain alcohol-dicarboxylic acid esters, polyol-linear and/or branched monocarboxylic acid esters, linear and/or branched monocarboxylic acid-monoalcohol esters, or mixtures thereof as desired. The synthetic ester blends based on these compositions are then mixed with a standard lubricant additive package to form the biodegradable 2-stroke lubricant.
Accordingly, it is an object of the invention to provide a synthetic ester basestock having improved biodegradability suitable for use in 2-stroke lubricant formulations.
Another object of the invention is to provide an improved 2-stroke lubricant basestock based on polyneopentyl polyol based synthetic esters.
A further object of the invention is to provide an improved 2-stroke lubricant basestock including polyneopentyl polyol esters and a coupling agent to increase solubility of standard lubricant additive packages in the blend.
Yet a further object of the invention is to provide an improved 2-stroke lubricant basestock including polyneopentyl polyol esters and coupling agent admixed with additional high molecular weight esters for adjusting the viscometrics of the lubricant.
Yet another object of the invention is to provide an improved biodegradable polyneopentyl polyol ester based synthetic ester blend which provides the desired viscometrics, low temperature properties, lubricity, miscibility with gasoline and solubility of additives in the finished formulation.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises a composition of matter possessing the characteristics, properties, and the relation of components which will be exemplified in the compositions hereinafter described, and the scope of the invention will be indicated in the claims.
The biodegradable 2-stroke synthetic ester basestocks and lubricants prepared in accordance with the invention are blends which include at least two synthetic esters. These esters are a polyneopentyl polyol (PNP) ester admixed with a coupling agent. The coupling agent is a molecule that increases the solubility of standard lubricant additive packages in the PNP ester based lubricant. The coupling agent is a compound of intermediate polarity between a hydrocarbon and the polyneopentyl polyol ester, such as esters having an oxygen content from about 4 to 16 weight percent, preferably from about 7 to 13 weight percent. In order to attain the desired viscosity, pour point, flash point and other properties of the final basestock blend, one or more additional esters such as a polyol ester of a linear and/or branched chain monocarboxylic acid, a dicarboxylic acid ester of a linear and/or branched chain monoalcohol, or a linear and/or branched monocarboxylic acid ester of linear and/or branched chain monoalcohols, or mixtures thereof is additionally added to the PNP ester-coupling agent mixture.
In the preferred embodiments of the invention, the basestock is a blend of the PNP ester-coupling agent mixture and one or more esters chosen from:
(1) polyol esters of linear and/or branched monocarboxylic acids,
(2) dicarboxylic acid esters of linear and/or branched monoalcohols, and
(3) linear and/or branched monocarboxylic acid esters of linear and/or branched monoalcohols.
The polyols for forming the polyol esters of linear and/or branched monocarboxylic acids are those having from 3 to 8 carbon atoms. The monoalcohols utilized are those having from about 6 to 22 carbon atoms. The monocarboxylic acids have from 6 to 20 carbon atoms and the dicarboxylic acids from 6 to 18 carbon atoms.
The PNP ester-coupling agent mixture includes at least 50 weight percent polyneopentyl polyol esters. The neopentyl polyol utilized to prepare compositions in accordance with the invention is at least one neopentyl polyol represented by the structural formula: 
wherein each R is independently selected from the group consisting of CH3, C2H5 and CH2OH. Examples of such a neopentyl polyol include pentaerythritol, trimethylolpropane, trimethylolethane, neopentyl glycol and the like. In some embodiments of this invention, the neopentyl polyol comprises only one such neopentyl polyol. In other embodiments it comprises two or more such neopentyl polyols.
Preferably, the polyneopentyl polyol ester is the reaction product of a mixture of partial esters of the neopentyl polyol with a suitable monocarboxylic acid(s). When the neopentyl polyol utilized is pentaerythritol, the polypentaerythritol moiety of the reaction product (xe2x80x9cpoly PExe2x80x9d) includes pentaerythritol, dipentaerythritol, tripentaerythritol, tetrapentaerythritol, etc. The reaction products are formed by reacting pentaerythritol with at least one monocarboxylic acid having from about 5 to 18 carbon atoms in the presence of an excess of hydroxyl groups relative to carboxyl groups. Subsequently, the partial esters are reacted with excess monocarboxylic acid(s) to obtain the polyneopentyl polyol ester. Most preferably, the acid moieties in the polyneopentyl polyol esters have from 7 to 10 carbon atoms and are linear. In the most preferred aspect of the invention, the acid component of the polyneopentyl polyol ester is a linear monocarboxylic acid, or a mixture of linear monocarboxylic acids, which contain up to about 5 weight percent or less branched chain acids.
Suitable acids for forming the polyneopentyl polyol esters include, but are not limited to, valeric acid, oenanthic acid, caprylic acid, pelargonic acid, capric acid, and isostearic acid. Preferably, the straight chain acid is a mixture of heptanoic (C7) and caprylic-capric (C8-C10). The caprylic-capric acid is usually identified as being a mixture of 8 and 10 carbon atom acids, but actually includes C6 to C12 acids, including trace amounts of C6 (generally less than about 5 weight percent) and less than about 2% of C12. Use of only linear acids to prepare the esters increases the biodegradability and viscosity index of the resulting polyneopentyl polyol ester.
The initial stage of the reaction to form the PNP esters is conducted in the manner described by Leibfried in U.S. Pat. No. 3,670,013 and in commonly assigned U.S. Pat. No. 5,895,778. The descriptions of both patents are incorporated herein by reference. Here, when pentaerythritol is the neopentyl polyol, a reaction mixture of pentaerythritol (272 w) and valeric acid (217 v) is placed into a reactor with extra valeric acid (38 v) in a receiver to assure a constant level of valeric acid in the reaction mixture. The mixture is heated to a temperature of 171xc2x0 C. and concentrated sulfuric acid (1.0 w) diluted with water (2 v) is added. The reaction mixture is heated to 192xc2x0 C. and maintained until 50.5 v of water is removed after about 1.4 hours. The Leibfried analysis of the product shows pentaerythritol, dipentaerythritol, tripentaerythritol and tetrapentaerythritol at weight ratios of 34:38:19:8.
In the present case, the polypentaerythritol partial esters are prepared by introducing a reaction mixture of pentaerythritol and a linear monocarboxylic acid having from 7 to 12 carbon atoms in an initial mole ratio of carboxyl groups to hydroxyl groups of about 0.25:1 to about 0.5:1 and an effective amount of an acid catalyst material into a reaction zone as described in the Leibfried patent.
When the PNP esters are prepared for use in the blends in accordance with the invention, the neopentyl polyol and selected acid or acid mixtures are mixed in the presence of a strong acid catalyst and heated. The reaction is continued until the desired viscosity of the reaction mixture is reached. At this point when the starting neopentyl polyol is pentaerythritol, the mixture includes partial esters of pentaerythritol, dipentaerythritol, tripentaerythritol, tetrapentaerythritol and the like. In order to complete the esterification of the partial esters, an excess of the acid or acid mixture is added to the reaction mixture which is then heated, water of reaction removed and acid returned to the reactor.
The acid catalyst is at least one acid esterification catalyst. Examples of acid esterification catalysts include mineral acids, preferably, sulfuric acid, hydrochloric acid, and the like, acid salts such as, for example, sodium bisulfate, sodium bisulfite, and the like, sulfonic acids such as, for example, benzenesulfonic acid, toluenesulfonic acid, polystyrene sulfonic acid, methylsulfonic acid, ethylsulfonic acid, and the like. The reaction mixture is heated to between about 150xc2x0 and 200xc2x0 C. while withdrawing acid vapor and water vapor to yield the poly(pentaerythritol) partial ester product.
Prior to esterifying the partial esters, the intermediate product will include a variety of condensation products of the neopentyl polyol. When pentaerythritol is the neopentyl polyol, the reaction mixture will include significantly more pentaerythritol than the 10 to 15 weight percent generally present in commercially available dipentaerythritol. Depending on the initial ratio of carboxyl groups to hydroxyl groups and selection of reaction conditions, the partial ester product may include the following components in the weight ranges specified in the following table.
The amount of the preferred heptanoic and caprylic-capric acid mixture for preparing the polyneopentyl polyol esters may vary widely. Initially, an excess of hydroxyl groups to carboxylic acid groups is present to form the partial esters of the neopentyl polyol, such as partial esters of pentaerythritol, dipentaerythritol, tripentaerythritol, tetrapentaerythritol, etc. The excess of hydroxyl groups is necessary to promote the polymerization of the partial esters. The molar ratio of acid mixture to the polyol can be varied depending on the desired degree of condensation and the ultimate desired viscosity of the lubricant. After formation of the partial esters, generally, a 10 to 25 percent excess, with respect to hydroxyl groups, of the mixture of heptanoic acid and C8-C10 acid is added to the reactor vessel and heated. Water of reaction is collected during the reaction while the acids are returned to the reactor. The use of a vacuum will facilitate the reaction. When the hydroxyl value is reduced to a sufficiently low level, the bulk of the excess acid is removed by vacuum distillation. Any residual acidity is neutralized with an alkali. The resulting polyneopentyl polyol ester is dried and filtered as described in Example 1 below.
The coupling agent, which is mixed with the PNP ester to form the PNP ester-coupling agent mixture, is a compound of intermediate polarity between a hydrocarbon and the polyneopentyl polyol ester, such as esters having an oxygen content from about 4 to 16 weight percent, preferably from about 7 to 13 weight percent. In the preferred embodiment of the invention the coupling agent is an ester which is the reaction product of a dicarboxylic acid having between about 18 to 36 carbon atoms and a monoalcohol having between about 6 to 13 carbon atoms. Most preferably, the coupling agent is a dimer acid ester which is the reaction product formed by the esterification of dimer acid with a monoalcohol, such as 2-ethylhexanol. Preferably, the dicarboxylic acid is dimer acid prepared from oleic acid which is heated to form the dimer, a 36 carbon diacid which results from a Diels-Alder type reaction. The 36 carbon dimer acid is then esterified with a branched chain monoalcohol having from 6 to 13 carbon atoms and preferably, 6 to 10 carbon atoms. In the most preferred embodiment, the monoalcohol is 2-ethylhexanol which forms di-2-ethylhexyl dimerate as described in Example 2 below.
The initial PNP ester-coupling agent mixture for the basestock is formed by mixing the polyneopentyl polyol esters together with the coupling agent, such as the dimer acid ester. Generally, at least 50 weight percent, and preferably 55 to 80 weight percent of the polyneopentyl polyol ester is admixed with between about 20 to 45 weight percent of dicarboxylic acid ester to form the PNP ester-coupling agent mixture. In the most preferred aspects of the invention, the initial PNP ester-coupling agent mixture is between about one to three parts and most preferably about two parts PNP ester to one part dicarboxylic acid ester by weight. Conventional lubricant additive packages are generally soluble in this PNP based ester mixture. However, additional esters may be blended with this mixture to provide desired lubricant properties.
The additional esters blended with the initial PNP ester-coupling agent mixture yield basestocks having desired viscometric properties. The additional esters are (1) polyol esters of linear and/or branched chain monocarboxylic acids, (2) dicarboxylic acid esters of linear and/or branched chain monoalcohols, (3) linear and/or branched monocarboxylic acid esters of linear and/or branched monoalcohols, or (4) mixtures thereof. Generally, the PNP ester-coupling agent mixture is present in the basestock blend at between about 60 to 90 weight percent with the additional esters present at between about 10 to 40 weight percent, based on the total weight of the basestock. In the most preferred aspects of the invention, the basestock includes a PNP ester-coupling agent mixture in an amount between about 65 to 85 and most preferably about 70 to 80 weight percent, with the balance being additional ester.
The additional ester may be a single ester or mixture of esters. The additional esters may be esters of a polyol and linear and/or branched chain monocarboxylic acids. The polyol may be a neopentyl polyol as described above and the monocarboxylic acid will have from about 5 to 20, and preferably 6 to 18 carbon atoms. A preferred example of the polyol is trimethylolpropane and a preferred example of the acid is oleic acid with the resulting ester being TMPtrioleate.
The additional ester may also be an ester of linear and/or branched chain monoalcohols and dicarboxylic acids that can vary depending on the specific properties desired. The branched chain monoalcohols utilized to form the esters will have from about 9 to 15 carbon atoms and are esterified with dicarboxylic acids having from about 5 to 12 carbon atoms, such as sebacic acid and adipic acid. Examples of preferred esters are diisotridecyl sebacate and diisodecyl adipate.
When the additional ester is a mixture of diisotridecyl sebacate and diisodecyl adipate, the diisotridecyl sebacate will be present in amounts between about 50 to 70 weight percent, preferably about 55 to 65 weight percent, and most preferably about 60 weight percent of the additional ester mixture. The balance is between about 30 to 50 weight percent diisodecyl adipate, preferably between about 35 to 45 weight percent, and most preferably about 40 weight percent of the additional ester mixture.
When the ester is formed from a monoalcohol and a monocarboxylic acid, the monoalcohol will have from about 6 to 20 carbon atoms and the monocarboxylic acid will have from about 6 to 22 carbon atoms. In the most preferred embodiment, the alcohol is 2-ethylhexanol and the acid is oleic acid with the resulting ester being 2-tethylhexyloleate.
The lubricant basestock is prepared by blending the polyneopentyl polyol ester and coupling agent mixture with the additional ester or ester mixture. The additional esters will be present in amounts between 10 to 40 weight percent, preferably between about 20 to 30 weight percent. In a preferred aspect of the invention, a typical composition will be as follows:
In another preferred embodiment of the invention, the additional ester is an ester of a high molecular weight monocarboxylic acid having from 16 to 20 carbon atoms and a branched chain alcohol or polyol having from 5 to 10 carbon atoms. In this preferred embodiment of the invention, the additional ester is a blend of 2-ethylhexyl oleate and trimethylolpropane trioleate. When these preferred esters are utilized as the additional ester, the trimethylolpropane trioleate ester is present in amounts between about 45 to 75 weight percent of the additional ester and preferably 60 to 70 weight percent, with the 2-ethylhexyl oleate present at between about 25 to 55 weight percent, and preferably 30 to 40 weight percent. In the most preferred embodiment of this aspect of the invention, the basestock will include the following:
Biodegradable 2-stroke lubricants, including the ester basestocks prepared in accordance with the invention, are prepared by mixing a conventional additive package in the synthetic ester basestock in conventional concentrations. Suitable lubricant additive packages are described in detail in U.S. Pat. No. 5,674,822, the disclosure of which is incorporated herein by reference. Such additives are generally added in amounts ranging from about 1 to 15 percent by weight, based on the total weight of the composition.
In order to be acceptable as a basestock for a 2-stroke lubricant, the basestock should meet the following typical specifications:
A key feature of a basestock and lubricant for 2-stroke engines is biodegradability. As noted above, biodegradability as measured by ASTM-5864 in excess of about 60% is generally considered acceptable. In all cases, standard lubricant additive packages must be compatible in the ester basestock blend, which in turn must be miscible with gasoline. Typical lubricant additive packages are generally not fully compatible with polyneopentyl polyol esters. However, upon appropriate blending of the initial PNP ester with a coupling agent, such as dicarboxylic acid esters, the additive packages are then sufficiently compatible with the blend so that the polyneopentyl polyol esters so that they can be utilized in large percentages in these 2-stroke lubricant formulations. The additional ester mixtures that are blended together with the PNP ester-coupling agent mixture are added to adjust and provide the desired viscometrics, such as high viscosity index and low pour point, a high flash point and also to provide a high degree of lubricity, good biodegradability and compatibility with the lubricant additive packages.
The invention will be better understood with references to the following examples. All percentages are set forth in percentages by weight except when molar quantities are indicated. These examples are presented for purposes of illustration only, and are not intended to be construed in a limiting sense.
The reactor in each preparatory example is equipped with a mechanical stirrer, thermocouple, thermoregulator, Dean Stark trap, condenser, nitrogen sparger, and vacuum source. The esterification may or may not be carried out in the presence of esterification catalysts, which are well known in the art.